1. Field Of The Invention
The present invention relates to electrostatic discharge (ESD) protection for electronic and other components, including electrically-programmable user-programmable interconnect elements and to microcircuits and other structures containing a plurality of components to be protected. More particularly, the present invention relates to structures for protecting the microcircuits, and particularly user-programmable interconnect elements and other components contained thereon, from electrostatic discharge (ESD).
2. The Prior Art
Protection of electronic devices from damage due to ESD is imperative for most electronic devices. In the case of transistors and integrated circuits, the protection is typically provided by specialized transistors, diodes, capacitors and resistors which are added to the portions of the integrated circuit which are likely to be exposed to ESD. Some types of circuits, however, do not have these types of components available to use as protection devices. Examples of these types of circuits include some types of programmable devices, multichip modules, hybrids, thin film circuits or flat panel displays. These types of devices would greatly benefit from a type of ESD protection device fabricated from thin film devices which would protect these circuits from ESD damage.
Electrically-programmable user-programmable interconnect elements are finding increasing usage in microcircuits of all kinds, ranging from integrated circuits to complex interconnection matrices. One popular type of electrically-programmable user-programmable interconnect element is known as an antifuse. An antifuse is basically two conductive electrodes which are separated by an antifuse material which is initially essentially non-conductive. Applying a programming voltage potential across the two conductive electrodes causes a disruption in the antifuse material resulting in a low-impedance conductive path between the two conductive electrodes.
Because the antifuse programming mechanism is essentially a voltage dependent phenomenon, unprogrammed antifuses are susceptible to ESD damage caused by static charge buildup across the two conductive electrodes. Static charges can create enough of a potential difference across the two conductive electrodes to result in the inadvertent programming of antifuse devices. Antifuse devices must be protected from voltages which meet or exceed the programming voltage; however, the protection must also allow the user to apply the programming voltage when desired and must not otherwise interfere with desired programming.
Several schemes are known in the prior art for protection of antifuse devices from static charge buildup during manufacturing, shipping, testing, and handling of the microcircuits containing the antifuse devices. For example, U.S. Pat. No. 4,941,028 to Chen et al. discloses both an active MOS transistor switch for discharging static voltage buildup and a thin oxide region overlying a diffused region providing a weakened region which will preferentially rupture prior to the voltage reaching a magnitude which will harm the thin dielectric regions associated with antifuse devices which it is designed to protect. U.S. Pat. No. 4,786,956 to Puar discloses an integrated circuit with active circuit components to protect the thin gate dielectrics associated with input circuits in integrated circuits.
While the prior art structures are useful to minimize certain ESD damage caused to structures such as antifuses, there remains room for improvement in such protection structures. For example, there is often a requirement for multiple handling of the microcircuit devices as they are tested and stored during the numerous operations which occur prior to shipment of the devices to customers who will ultimately program them. Each step of this process carries the potential for ESD damage to the antifuse devices. ESD protection devices for antifuses must be disabled to test or otherwise use the microcircuit device, and known prior art protection devices are irreversibly disabled, prohibiting complete protection in an environment in which multiple tests separated by handling and/or storage periods are required.
In addition, there are some antifuse applications which do not permit the use of active transistor protection devices, such as applications where the antifuse elements are disposed on an insulating substrate which does not allow for the fabrication of active devices thereon. In such situations only passive protection devices may be employed.
Finally, certain other electronic components, such as flat panel displays, and certain mechanical components, which contain metal layers and dielectric layers, are also subject to ESD damage. Presently, panel displays are protected by hard-wire short circuiting the conductors of the display array to one another. When the panel is ready for installation, the shorting conductor is mechanically cut away from the structure. It would be advantageous to provide an electrically deactivated ESD protection device.